Wrack mostly consists of the kelp that washes onto beaches from the ocean. Wrack is an essential part of the ecology of the shoreline, providing food and habitat for everything from insects to birds.
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Mean density of two important members of the upper beach macrofaunal community — California beach hopper Megalorchestia californiana (red) and Alloniscus perconvexus (blue )— from surveys of eight beaches on Santa Rosa Island from 1994–2015. Curved lines represent statistically smoothed means. Figure: Channel Islands National Park